In many mammals placental development involves the invasion of the uterine mucosa by trophoblast, until the chorion has become intimately associated with the maternal blood supply for the purposes of physiological exchange. At present the factors which control trophoblastic growth and differentiation are incompletely understood. One major objective of this research will be to further elucidate the apparent role of maternal vascular components (particularly endothelial cells) in controlling trophoblastic development in at least some mammals. Two species of neotropical bats (Carollia and Molossus) in which interactions between the trophoblast and maternal blood vessels are unusually intimate and important will be used as the animal models. Trophoblast-maternal vascular interactions will be examined in lab-bred bats with histological, cytochemical and ultrastructural techniques in an effort to identify more precisely which uterine components may have a role in directing trophoblastic growth and differentiation. The other major goal of this research will be to develop Carollia as a small, convenient, and inexpensive animal model for studies of both implantation and placentation with relevance to humans. Like our own species, Carollia exhibits true menstruation, interstitial implantation which usually occurs preferentially within a restricted portion of a simplex uterus, highly invasive cytotrophoblast that rapidly penetrates the myometrium and probably induces physiologically important changes in the maternal blood supply to the placenta, a discoidal hemochorial placenta, and gives birth to a single well-developed infant after a long gestation period. For reasons which are not yet understood (in part because of the lack of appropriate animal models) trophoblast-vascular interactions are frequently abnormal in human pregnancies ending as spontaneous abortions or complicated by preeclampsia, other hypertensive disorders and/or fetal growth retardation. Studies presently in progress have established that some lab-bred Carollia also spontaneously exhibit retarded conceptus growth. In order to develop this bat as a model for further studies on implantation and placental development relevant to humans, these processes will be thoroughly characterized in lab-bred animals utilizing histological and ultrastructural approaches. Pregnant bats will also be maintained under different environmental conditions to determine if developmental delays can be experimentally induced or eliminated.